diff --git a/packages/opencode/src/session/compaction.ts b/packages/opencode/src/session/compaction.ts
index e5b42469..6af398f1 100644
--- a/packages/opencode/src/session/compaction.ts
+++ b/packages/opencode/src/session/compaction.ts
@@ -24,9 +24,11 @@ export namespace SessionCompaction {
 
   export function isOverflow(input: { tokens: MessageV2.Assistant["tokens"]; model: ModelsDev.Model }) {
     if (Flag.OPENCODE_DISABLE_AUTOCOMPACT) return false
+    const context = input.model.limit.context
+    if (context === 0) return false
     const count = input.tokens.input + input.tokens.cache.read + input.tokens.output
     const output = Math.min(input.model.limit.output, SessionPrompt.OUTPUT_TOKEN_MAX) || SessionPrompt.OUTPUT_TOKEN_MAX
-    const usable = input.model.limit.context - output
+    const usable = context - output
     return count > usable
   }